Tube tester



Oct. 10, 1961 R. A. REID 3,004,213

TUBE TESTER Filed Sept. 5, 1958 6 Sheets-Sheet 1 lo 0 N OFF 30 D? N RL 2'! SHORT TUBE TEST TgP gg RL|7 MARKER RECORDER I l a! LOW LIMIT RL GAS Rm z'gg METER RELAY RL MISTEPPER BR GAS ZERO RECORDER LIMIT za 9 BRIDGE /22 RL 2 EMISSION cur OFF RL4 STEPPER 7 RL 5 L RECORD BR'DGE METER RELAY G I STE PPERS INVENTOR Robert A. Re i0 ib/(gym f 2? ATTORNEYS R. A. REID TUBE TESTER Oct. 10, 1961- 6 SheetsSheet 2 Filed Sept. 5, 1958 INVENTOR Po [2 er Z A. Reid R. A. REID TUBE TESTER Oct. 10, 1961 6 Sheets-Sheet 3 Filed Sept. 5, 1958 REJECT REJECT COUNTER CUT OFF INVENTOR Po berz A. Fe in 6%NEYS R. A. REID TUBE TESTER Oct. 10, 1961 e Sheets-Sheet 4 Filed Sept. 5, 1958 52:8 Swim 6 53 Om E wlw

INVENTOR Poberz A. Reid R. A. REID TUBE TESTER 6 Sheets-Sheet 5 Filed Sept. 5, 1958 ww! um h n31 m N INVENTOR Poberz A. Pe/o ATTORNEYS R. A. REID TUBE TESTER Oct. 10, 1961 6 Sheets-Sheet 6 Filed Sept. 5, 1958 vNJm mm 5 ok Hum- E ATTORNEYS United States Pattit C TUBE TESTER Robert A. Reid, Atlantic Highlands, N.J., assignor to Thomas Electronics Inc., Passaic, N.J., a corporation of New Jersey Filed Sept. 5, 1958, Ser. No. 759,I61 Claims. (Cl. 32423) This invention relates to tube testers and more particularly is concerned with a production type automatic tester for checking several parameters of cathode ray tubes. I

At the present time, there is no suitable equipment available on the market for automatically testing mass produced cathode ray tubes. The present procedure is to employ an operator or a series of operators near the end of the production line for, manually taking readings of themore important tube characteristics such as the emission cut-cit, and gas ratio as the cathode ray tubes pass along the assembly line. Ordinarily the operator makes an individual reading for each parameter being considered. The operator then has a chart which he must consuit in order to decide whether or not. the particular tube under consideration is to be reiected'. Due to the unavoidable human error factor, many tubes thus passed by the operators maybe faulty in any of one or several respects. Similarly, there isconsiderable; temptation on the part of individual operators to pass tubes having border-linecharacteristics which, in fact, may not be suitable to be placed on the market for general consumption. by The novel tube tester of the present invention is designed for process control testingand quality control evaluation forindustry. A The tester is fully automatic and may require no operator when used with conveyorized operation. It may be used to measure shorts, to check total emission and cut oft characteristics of the tiibe as well as gas ratio vs. emission characteristics. The tester provides output. sources for automatic recordings of all the above-mentioned metered parameters for a permanent production record and for use in product evaluation. In addition, the present invention roughly halves the time required per tube for making thesetests.

Major features oi the present invention area series of balancing networks, a plurality of low limit meter relays providing for the immediate rejection of tubes failing to meet certain pre -determined conditipns and a series of stepper relays for balancing outvarious tube parameters which permit anaccurate recording of the cathode ray tube characteristics in discrete stepvalues particularly suited for use in conjunction with digital display equipment, Q i

lftis accordinglyone object ot thepresent invention to provide a fully automatic device for testing cathode ray tubes. g

Another object of the present invention is to provide an automatic tube tester for conducting aplurality of checks on cathode ray tubes.

sun another object of the .p resent invention his provide a production line tester for cathode ray tube manufacturers which provides for automaticrecording of all metered, parameters for use in conveyorized operations. 4

An additional object of the present invention is to pro vide, a cathode raytube testing unit which rcduces to one-half the time required for testing each tube.

These andfurtherobjects and advantages of the invention will become apparent upon reference to the following specification, claims and appended drawings wherein: I In I i FIGURE 1 is an overall block diagram showing the interconnection of the major components of the tube tester of the present invention and indicating the time sequence of asingle testing cycle.

I Patented Oct. 10, 1961 ICC tube tester of the present invention employed in checking for interelectrodeshorts;

FIGURE 3 is a circuit diagram of a portion of the tube tester of the present invention, employed in checking the total emission current ofa cathode ray tube;

FIGURE 4 is a circuit diagram of a portion of the tube tester of the present invention used in obtaining the cut-ofi characteristics of a cathode ray tube; v

FlGURE 4A is a simplified illustration of strapping which may be employed between the emission and cutoli stepper switches to provide for the rejection of tubes having a satisfactory total emission with no grid voltage impressed but an unsatisfactory emission for the cut-elf exhibited;

FIGURE 5 is a circuit diagram of a portion of the tube tester tube testing unit employed to zero out stray leakages to enable the highly sensitive gas ratio circuit to give an accurate reading;

FIGURE 6 is a circuit diagram of another portion of the tube testing unit employed in obtaining the gas ratio characteristics of a cathode ray tube at a predetermined emission level;

FIGURE 7 is a circuit HGURE 8 tea diagram of a typical contact meter used in the various tests.

The several sheets of drawing represent the tube tester broken down into functional elements for simplicity of depiction and explanation. Certain relays, contacts, elements and subcircuits appear on more than one sheet of drawing since this facilitates easier following of the description of the circuits. interconnections between lines on the various sheets are indicated by the symbols on the sheets as is the custom with diagrams of this type. Descriptive letter and number reference characters are used in the customary manner of use of these skilled in the art in order to reduce the amount of descriptive matter necessary to a clear understanding of the operation of the unit. b b I Referring specifically to the drawings, in FIGURE 1 there is shown an overall block diagram of the major components of the tube tester of the present invention indicating the sequence of events involved in a single complete test cycle. The present invention is adapted for use in the mass production of cathode ray tubes in which a continuous series of cathode ray tubes enter a test room on a suitable conveyor. In accordance with current procedure, the tubes are carried face up on a conveyor carrier supported by a pair of parallel spaced rails; The carrier may be of the type disclosed in the assignees copendingapplicaticn Serial No.712,2.l9 filed January 3d,

1958. In the test room an assembler places a yoke' an'd socket on the tubes as they pass by. Further movement of the tubes through the test room to a testing station causes the conveyor passing over the rails to trip an oncyclemicroswitch, thus starting the sequence of test operation described below. b b k b As one of the cathode ray tubes to be tested, indicated at 14, reaches the test station the rails upon which the tube is conveyed pass over and trip an on microswitch 10. At the same time suitable means (not shown) may be provided for operatively connecting the tube tester to the various electrode pin connections of the tube, or if desired, the tube may be connected to the tester by hand.

As the tube comes into the test position, a short test relay RL27 is activated and the short test is made just prior to activation of the switch 19. If one or more shorts exist relay 35 is energized. This relay operates to completely stop the test cycle and in addition energizes a reject indicator and areject counter.

Subsequent to the short test the tube is automatically diagram showing the oil-cycle sequence of the tube tester of the present invention; and

coupled to an emission bridge 12 and undergoes a total emission test. The tester includes a low limit meter relay RL9 for immediately rejecting all tubes which do not possess a minimum amount of cathode emission. The bridge 12 is balanced out by an emission stepper switch and recorder RL which retains the emission reading for the remainder of the cycle.

After the emission test the tube undergoes a cut-off test. Such a test indicates the control the grid maintains over the cathode emission and records the negative bias voltage necessary on the grid to completely out oh the tube. The cut-on test involves a cut-off bridge 22, a low limit meter relay RL2 and a cut-oif stepper and recorder RL4.

The final test is the gas ratio test or the ratio of the ion current to the emission current when the tube is biased to draw about 500 microamperes of total current. This test also involves emission bridge 12, low limit meter relay RL9 and a gas ratio stepper and recorder RLid. If desired a conventional tube marker 11 may be connected to the gas ratio stepper and recorder unit to provide suitable legends on the tube at the end of a test cycle indicating that the tube is acceptable or satisfactory in having passed all the tests.

7 Short check As the tube comes to the test position, it is first placed into a short check test and the circuitry for accomplishing this is shown in FIGURE 2. This figure shows the cathode ray tube 14 connected into the circuit of the short check relays RL35AB, CD, EF, GH. Relays RLZZAB, CD, EF, the coils of which are shown in FIGURE 7, have contacts in FIGURE 2 which enter into the operation of this portion of the circuit. Referring for the moment to FIGURE 7, the test unit of the invention is made ready for operation by means of a manually operated switch 8 which is in series with the normally closed on cycle" switch 10. This switch in turn is connected to relays, RL6AB, CD, EF and the other side of RLfiEF is connected to the ground. The left side of manually operated switch 8 in FIGURE 7 is connected to a source of 24 volt D.C. through pins 1 and 4 of a relay RLitZA.

When the unit is placed into operation manually operated switch 8 is closed, thereby placing 24 volts on RL6 to energize that relay for a purpose presently to become apparent.

RL27 is at this time also energized through the off cycle switch 30 by a 24 volt D.C. supply. The oif cycle switch 30 is normally open and is closed at this time for reasons to be described in detail presently.

Turning to FIGURE 2, and recalling that relay RLZ7 is energized, RL27A has pin 1 in contact with pin 3, RL27B has pin 8 in contact with pin 6, RL27C is open, RLZ'i'D has pin 8 in contact with pin 6, and RL27E has pin i in contact with pin 3. Under these circumstances it will be seen that the cathode of CRT 14 is connected to ground through pins 1 and 3 of RL27A and through the coil of RL35GI-I. The first grid G1 of the tube is connected to a 4 and these are connected across manual switch 8 and on cycle switch 10 in FIGURE 7.

It will be recalled that on cycle switch 10 is a normally closed switch and that relay RL6 is initially energized when this switch is closed. As the tube advances to the short check test the on cycle switch is opened thereby de-energizing relay RL6. If, however, a short exists, switches 8 and 10 are shorted by contact pins 1-3 of one of the relays RLAB, CD, EF, GH so that relay RL6 remains energized and this prevents further operation of the test cycle as will become more apparent on reference to the following description of the operation of the emission check. If a short exists in the tube this fact is indicated by the reject light, is recorded by the counter, and the test cycle is halted until the tube is removed. If no short exists the unit automatically proceeds to the emission test.

Emission check Referring to FIGURE 3, there is shown a bridge circuit indicated generally at 12 having upper legs formed by the windings of relays RL7 and RLS. The lower left leg of the bridge is formed by the cathode ray tube, that is, this leg is connected to the cathode and second grid G2 of the tube. The lower right leg of the bridge is formed by a series of resistances which are selected by a stepper switch actuated by stepper switch relay RLSA. The two meters '13 and 15 in the lower legs of the bridge circuit are for -100 Volt DC. supply through the coil of RL35EF, I

pins 6 and 8 of RL27B, and pins 1 and 3 of RL2'7E. The second grid G2 is connected to a 315 Volt DC. supply through the coil of RL35CD, pins 6 and 8 of RL27D and RLlA (FIGURE 3). The fourth grid G4 is connected to ground through the coil of RLSSAB.

If not interelectrode short exists in the cathode ray tube 14, none of the relays RL35AB, CD, EF, GI-I will be energized. If, however, any of the electrodes are shorted, a relatively high voltage is placed across one or more of the relays RL35AB, CD, EF, GH to energize that relay and close its associated contact pins 13 and 6-8 which are otherwise open. The contact pins 6 and 8 of any of relays RL35AB, CD, EF, GH operate relay RL31 which calibration purposes.

When a positive voltage is applied to the top of the bridge circuit G2 current will flow to produce a voltage across the lower left leg of the bridge circuit. This may then be balanced by a voltage appearing across the selected resistances in the lower right hand leg of the bridge circuit. The balance or unbalance of the bridge is sensed by means of a conventional twin triode vacuum tube volt meter type circuit consisting of triode halves I7 and 19. As is well known, with the same voltage applied to the two grids, equal currents flow through both sections of the twin triode, the tube cathodes are at the same potential and no current flows between the terminals B and C. A pair of potentiometers 21 and 23 are provided in the circuit of the cathode of the left tube for the total emission and gas ratio emission tests respectively. The currents in the two tubes can be adjusted to balance by whichever potentiometer 21 or 23 is in the circuit at the time, in order to take care of variations in the tube sections.

The unbalance voltage appearing at terminals B--C is applied to the actuating coil 25 of a contact-type meter 27 shown in FIGURE 8. When this meter is in its rest position a contact is made between D and E and since E is connected to C this places a voltage on the left end of RL9 in the upper right corner of FIGURE 3, otherwise this meter reads the emission currents. The right hand portion of FIGURE 3 shows the connections of relays RL22, RLZS, RLl, RL12, RL6, stepper relay RLS, and RL19, whose functions will presently become more apparent in a description of the operation of the illustrated circuit.

in turn operates the total reject light and a conventional counter, not shown. The operation of any of the relays RL35AB, CD, EF, GH also closes pin fi -3 of the relay Recalling the operation of the short check test, it will be remembered that the on cycle switch is opened by a tube advancing to the test position. If a short exists in the tube, however, one of relays RL35AB, CD, EF, GH places a short circuit around the on cycle switch '10 to pins 1 and 3 of RL35 to keep energized relays RL6AB, CD, EF and stop the further functioning of the test unit.

Assuming that there is no short in the particular 'tube under test, and referring to FIGURE 3, relay through a smears relay RL8. Actuation of relay RL8 bypasses the meter 13 through RLSA to provide protection for the meter. .Relay RLIC in the lower right leg of the bridge circuit grounds the bank of resistors which are selected by the stepper switch RLSA to complete the bridge circuit.

The bridge circuit will now be unbalanced by an amount which is a function of the emission of the tube. The unbalance of the bridge circuit causes the contact meter 27 to move up-scale thereby opening the contact between D and B so that the left side of relay RL9 in the upper right corner of FIGURE 3 is floating. The prior energization of RLID has closed a 100 volt circuit to relay RL22, but the contacts of this relay do not close before the meter moves upscale by reason of the capacitor across the relay coil which provides a time delay. It is thus possible for an operatorto read the emission of the tube from the meter without Wait :ing for the balancing operation to occur. 7 I When relay RL22 is energized the right end of relay RL9 is grounded and a second set of contacts RLZZB is opened to de-energize relay RLZS. A time delay is provided in the release of the contacts of this relay in order to allow the cathode ray tube emission to stabilize before the balancing operation occurs. When re- .lay RLZS is finally de-energized, its contacts RLZSB energize RLIZ through the contacts RLZSB, RLllB and RL32 to 24 volts received from RLdB. Energizetion of RL12 establishes a 24 volt supply to relay RL19 through RLIZA and RL15. Relay RL19 in turn con- .trols operation of the stepper relay RL5.

The stepper relay RLS steps the movable arm of the stepper switch around in a conventional manner to sweep the resistances connected to the switch. When the stepper relay RLS reaches the correct resistance necessary :to balance the bridge circuit, the contact meter returns :to its 'at-rest or zero reading, closing the contacts be- :tween I) and E to thereby energize relay RL9. This energizes relay RL32 which opens the supply circuit to relay RL12. The contacts of relay RLlZA move from pin 3 to pin 4, thus removing '24 volts from relay RL19. The stepper relay RLS remains energized, however, due to the magnetic bypass contacts indicated at pins 1 and 4 and this holds the stepper at its final position so that the reading may be recorded. Relay ELIZA, in addition to deenergizing relay R1419, rechergizes relay 111.6 and contacts RL6B (ls-energize relay R121. As a result the relays are all returned to their original positions and the total emission check has been fully accomplished.

Cutofi check Another test incorporated in the cathode ray tube tester oithe present invention is the so-called cutoii emission check or more simply the cutoff check. To be acceptable the cathode current of the tube must be cut otf, i.e., reduced to zero when a certain predetermined range of cutoll voltage is applied to the first grid G1 of the tube. This test is accomplished by the circuitry shown in FIGURE 4.

The cutoff check involves a second bridge circuit indicated generally at 22 including the two halves of a twin triode labeled 2 3 and 25. In this arrangement the grid of tube half 23 is connected to ground. The grid of tube half 25, on the other hand, is grounded one megohm load resistor 29. In addition the ungrounded side of load resistor 21' is connected to the cathode of CRT 14. p I In the operation ofthis' circuit grid G1 of the cathode ray tube is initially at zero potential. In this case the emission current of the cathode ray tube 14 passes from the cathode through load resistor 26:. Since load resistor 20 is connected to the grid of tube half 25 the emission current potential developed across load resistor 20 is applied to the grid and causes tube half 25 to draw more current than tube, half 23. The resulting unbalper switch RIA applies increasing negative bias in two volt steps to the grid G1 of CRT 14. The volt meter 29 may be incorporated in the grid G1 circuit for the purposes of calibrating thestepper relay switch deck RL4A. As increasing negativebias is applied to grid G1 of the CRT, the tube approaches cut off and draws less current through its cathode. This resultsin a decrease in current through load resistor 20 and a reduction in the positive bias applied to the grid of tube half 25. When the voltage applied to the grid of the CRT from stepper switch deck RL4A reaches cutoff, the cathode current is zero and no bias potential is developed across load rejsistor 20. When thishappens the tube halves 23 and 2.5 are balanced and no signal is applied to meter relay RLZ.

v A second stepper switch deck RL4B is driven in synchronism with stepper deck RLQA by stepper switch RL4 scribed acted to move RL6C (FIGURE 4) from pin 4 to pin 5. This removed the short to ground previously existing across load resistor 20 and connected this resistor into the grid circuit of tube half 25. With load resistor 29 in the grid circuit of tube half 25 and also in the cathode circuit of CRT 14, the bias potential developed across resistor 20 causes an unbalance between the two halves 23 and 25. As a result the tubes draw diilerent currents and the potential developed across their respective cathode resistors is unequal. The potentiometer 27 is provided for adjustment of the original bridge balance. The unbalance signal is in turn applied to pins B and C of meter relay RLZ, the latter pin being in turn directly connected to pin E of this relay.

Movement of the arm on RL6C from pin 4,to pin 5 in addition serves to apply 24 volts to relay RL3 thus energizing this relay. With the unbalance voltage applied to meter relay RLZ and indicated by that meter the contacts RLSB are closed connecting contact D of'the meter relay to ground through the coil of RLZ. Since the indicator or pointer of R12 is deflected to give the unbalance reading, contact D, of the meter as is more clearly indicated in FIGURE 8, is disconnnected from contact E and hence the coil of RL2 remains unenergized. Relay RLSA in moving from pin 4 to pin 3 supplies 24 volts to a delay relay RL34 by way of contacts RLS I, RL27F, and RL30. Relay 34 includes a capacitor 31 providing a delay which allows the reading on meter relay RLZ to be independently read if so desired. H

Relay RL34 in turn actuates stepper relay coil RL4. A variable resistor 33 is included in the stepper circuit for controlling and adjusting the speed of stepper relay RM. Upon energization of the stepper relay RL4 the stopper switch decks RIAB and RL4A sweep over the indicated positions until cut-off bias is reached, At this point no potential is applied to the grid of triode half This results in the energization of the coil RLZ and the operation of this relay. Closing of relay RLZ grounds one end of relay RL30 which is thereby energized. The movement of the contact of relay RL30 away from pin breaks the 24 volt supply circuit to relay RL34 which in turn de-energizes stepper relay RL4. This stops the stepper relay causing deck RL4B- to remain at the position indicating the value of voltage required to cut oil CRT 14.

Provisions are included in this circuit for completely rejecting a tube having a cutofl value that is either below or above a predetermined range of values. This is accomplished through a third stepper switch deck RLAE. Relay stepper switch deck RL4E moves in conjunction with stepper decks RL4A and RL4B as increasing bias voltage is applied to the grid G1 of the CRT. A tube having a low cut-off value will be unable to produce suflicient unbalance in the triode tube halves 23 and 25 to drive the sweeper arm of RL4E beyond the first position indicated at A in FIGURE 4. As a result the 24 volts supplied to the stepper sweeper arm of deck RL4E through RL27I will pass by way of contact A of stepper deck RL iE to pin 3 of RL30. Pin 3 is at that time in contact with pin 1 inasmuch as RL30 is energized through RL2. That is to say, the meter relay has moved up scale and then has moved down scale as the unbalance was reduced and has locked in contacts RLZ. The movement of the stepper switch which occurred to balance the bridge, however, was not enough to carry the arm of deck RL4E past position A (which obviously may be made as extensive as desired). Thus 24 volts is fed to relay RL 37 energizing that relay. Contacts RL37A of this relay close completing the circuit to a low cutofi counter while contacts RL37B energize a total reject counter.

Similarly it the CRT 14 cuts oit at too high a voltage, the sweep arm of stepper switch deck RL i-E will sweep over all 26 positions indicated and come to rest on the contact indicated at Z. This results in the energization of relay RL38B through relay RL27G. Relay RLSSAB through pins 6 and 8 operates a total'reject counter, and through pins 1 and 3 operates a high cut ofi counter.

By a proper predetermined strapping between stepper deck RL4E and emission stepper deck RLSE, the latter stepper can be utilized to give an indication of low emission during the cut off check. It sometimes happens that a tube will pass the total emission check shown and described above with reference to FIGURE 3 and yet possess insuflicient emission to correspond to its cut-oft: voltage.

That is to say, the total emission test is applied with zero voltage on the first grid G1 and while the total emission indicated may be satisfactory for a certain range of cutoif voltages it is not adequate for the higher negative voltage necessary to produce cutofi in the particular tube. A simplified illustration of the principle relied upon is shown in FIGURE 4A. Referring to that figure simplified decks RLSE and RL4E are shown with only 5 positions each. If it is determined that a CRT with a cut-oif which drives the stepper RL4E to at least position 2 should have an emission driving the stepper RLSE to at least position 3, then position 2 on RL4E is strapped to positions 1 and 2 on RL5E. Thus, it will be seen that when the arm of RLSE is not past position 2, a circuit through RLSE and RL iE will be completed for all tubes which have a cut-off driving the arm of RL4E as far as position 2. When this happens 24 volts supplied by way of RL27l passes through RLdE, RLSE to energize relay RL29. The operation of relay RL29 acts through pins 1 and 3 to place 24- volts on relay RLfilt operating a total reject counter and a total reject light. RLBi. also opens pins 1 and 4 thereof (bottom of FIGURE 4) to deenergize RL34 and thereby stop the stepper RL4.

Gas ratio check Gas ratio zero is used to balance out leakages that exist in the equipment and tube prior to the gas ratio reading. The gas ratio zero circuit is shown in FIGURE 5 and 8 involves a third balancing network indicated generally at 38. Balancing circuit 38 includes twin triode halves 35 and 37. In this arrangement a negative bias of minus volts DC. is applied to the anode of the CRT through a load resistor 26. In addition the CRT anode side of load resistor 26 is connected to the grid of triode half 35. The leakage current flowing through the CRT 14 and collected at the anode passes through load resistor 26 causing an unbalancing bias to be applied to the grid of tube half 35 unbalancing the twin triode. The unbalance voltage developed at the cathodes of tube halves 35 and 37 is applied by way of terminals B and C to a meter relay RLZl. A second meter relay RL23 is connected in the meter relay circuit for the purpose of protecting meter relay RL21 from overload and rejecting high current tubes. Both meter relays are of the same type as illustrated in FIGURE 8.

Unbalance of the twin triode halves 3'7 and 35 actuates a relay RL17 driving stepper switch deck RLiiA stepwise over a series of 100 ohm resistors. A second stepper deck RL17B is used to return the stepper switch to the home position after the test cycle, through RLldC. Stepper relay deck RLliA is connected in the plate circuit of the triode halves 35 and 37 and as the sweep arm moves across the 26 positions indicated RL17A reaches a position in which the currents flowing through the cathode resistors of triode halves 3'5 and 37 are equal. The value of plate resistance inserted by stepper deck RL17A necessary to balance out the unbalanced bias applied to the grid of tube half 35 by the leakage current flowing through CRT 14 is an indication of the leakage current flow through the tube with cut-off bias on the grid G1;

Proceeding now to a detailed description of the operation of this circuit, the activation of relay at the end of the cut-oil check described above serves to energize relay RLld. This is accomplished through contact RLSOB, pin 6, as indicated in FIGURE 5. With the closing of relay RLltl contact RLitlA applies 24 volts to pin 1 of contact RLiiiA for purposes to he more fully described below in connection with gas ratio check. Contact RLlilB removes the short from around load resistor 26. The leakage current potential developed across load resistor 26 is consequently applied to the grid of tube half 35. Contact RLltlC applies minus 100 volts to relay RLZG bringing this relay into operation. Contact RLI'GD completes a circuit through relay coil R1223 from protection meter RL23. However, since protection meter relay RL23 is connected for bi h limit operation no connection is made between terminals A and E thereof in the absence of meter energization in excess of the high limit. (See FIGURE 8). Thus While RLZS is deflected under the unbalance signal received from terminals B and C of the cathodes of tube halves 35 and 37 the coil of relay RL23 remains unenergized. Similarly contact RLZQB closes a circuit to the coil of meter relay RLZl which remains unenergized inasmuch as the upscale movement of the meter has broken contact between terminals D and E thereof. (See FIGURE S.) Contact RLZ-QA applies 24- volts received from contact RLfiB through relay contacts R153 and RLi'i to relay R1424, The contacts of RLZ activate stepper relay RLl? driving stepper decks RL'l7A and RLlYB. A capacitor 24a is provided across relay RL24 to provide a time delay to allow the meters to give an accurate reading as in the preceding bridge circuits.

In the event of a short or an extremely gassy tube, protection meter relay RL23 will be overloaded and its internal contact will close a circuit between its terminals A and E. This completes the circuit through the coil of RL23 activating this relay. Contacts RL23A in closing provide a short across the input terminals B and C of meter relay RLZl thereby protecting this relay. In addition contacts RL23B close to operate a gas ratio zero light and counter through relay RL40 and a total reject light and counter through relay RLSiB.

If the CRT 14 under test passes the gas ratio zero check, stepper relay switch RLIIA will reach a position in which leakage current flow is balanced out by the plate resistance in the triode halves 35 and 37.. When the signal across terminals B and C reaches zero, the internal contacts of meter relay Rial will close a circuit between its terminals D and E energizing the relay coil RL21. Relay R1221 in turn operates relay 111.33 which in turn removes the 24 volt energizing potential from relay RL24. Relay R3224 includes a delay capacitor 24a and a speed control potentiometer similar in operation with that de scribed with respect to the total emission check and cut- "oii check. De-energization offRL24 deactivates stepper relay Rial? thus stopping the arms of stepper decks RLlt'TA and RLlf/B. Since relay RL17 includes a magnetic bypass contact 41 stepper relay switches RL17A and RLIIB do not return to the home position but retain the balance position. Specifically, stepper deck RLI'IA "stays at a position at which the plate resistance balances out the leakage current applied to the grid of tube half '35.

In the gas ratio zero check described above the bridge circuit 38 was balanced to cancel out the portion of the leakage current iiow existing with cut-off bias on the grid concerns the ratio of the ion current to the cathode emission current drawn by grid G2 when the bias on grid G1 of the tube being tested is sufficient to draw 'a current of approximately 500 micro amperes.

' G1. The gas ratio emission test now to be described I As can be seen in FIGURE 6 the operation of rel'a'y RL33 at the end of the gas ratio zero check described above in moving from pin 4 to pin 3 applies 24 volts through relay RLilE to energize this relay. Contact RL18A completes the circuit to relays RLlS and RL11.

Contacts RLllD in turn place a short around load resistor 2i and connect the cathode of CRT 14 to ground. The contact of RLIIA moves from pin 4 to pin 3 operating relay RLI which closes the original emission bridge circuit 12 of FIGURE 3. In addition as shown in FIG- URE 3 RLHC transfers the lower right hand arm of bridge 12 to a separate resistor 42 adjust d to draw 500 microamps from the bridge source by a variable resistor 43. As a result of the operation of relay RLl, cathode ray tube 14 is again connected in the lower left hand I arm of bridge circuit 12 of FIGURE 3 by way of grid G2 and the grounded CRT cathode. In addition contact RLlSA connects a gas ratio emission bias stepper deck RLl lA to the grid G1 of CRT 14. (See FIGURE 6.)

As can be seen from the connections already described the gas ratio emission check involves the balancing bridge '12 ofFIGURE 3 which was also used to measure total emissionas previously described. Meter relay RL9 likewise serves both the total emission check and the gas ratio emission check. In operation the CRT is connected into thelower left arm of bridge 12 through the grid G2 and the cathode. At the same time the negative bias of 100 volts remains applied to the anode so that the tube draws ion current. In addition stepper deck RL14A connected into the grid G1 of CRT 14 as indicated in F GURE 6 sweeps through a series of resistors to apply increasing steps of negative bias to the first grid of the cathode ray tube. The bias of the tube is in this manner increased until the total current drawn by the grid G2 of the tube reaches 500 micro amperes. When this value of current is reached the left arm of bridge 12 is balanced against the right arm containing resistor 42 previously adjusted by resistor 43 to draw 500' micro amperes of current. When the balance is reached the gas ratio emission value is indicated on a stepper deck RL14B which operates in conjunction with the bias stepper deck RL14A. Meter relay RL9 operates in a manner similar to that described in connection with the previous total emission test to give an initial indication of the bridge 10 unbalance. The delay incorporated by means of at ca pacitor in relay RL25 retards the operation of stepper decks RL14A and RL14B for a sufficient time to allow the meter relay RL9 indicator to stabilize. Likewise upon reaching balance the signal from terminals B and C by way of potentiometer 23 in the bridge 12 reaches zero and meter relay RL9 closes to actuate the coil of that relay.

In conjunction with the previously described actuation of relay RL18 to energize relays RL15 and RL11, contacts RL18B close to maintain energization of relay RL18 until the end of a complete measuring cycle. 'Thus contacts RL18B form a self locking arrangement for relay RL18. Relay contact RLIIB upon closing at the initiation of the gas ratio emission check supplies 24 volts to relay RL13 by way of RLZ-SB, RL32, and RL11A. Contacts'RLliiA energize the delay relay RLZS including a speed control'potentiometer 46. This latter relay serves to activate stepper'relay RL14.

With the balanced voltage reached and the internal contact of meter relay RL9 closed to place terminal D in contact with terminal E relay coil R L9 is energized to operate'relay RL32 as is best seen in FIGURE 3. Referring back to FIGURE 6, operation of relay RL32 breaks the 24 volt supply to relay RL13 in turn deactivating relays RL25 and RL14 and thus stopping the arms in stepper decks RLl lA and RL14B. At this point all the tests on the cathode ray tube are complete and the testreadings are recorded on the various stepper switches.

In FIGURE 7 is shown the circuitry and relays involved in readying the tube tester of the present invention for a new tube to be tested when the complete test of a first tube is at an end. This operation is commonly referred to as the olf cycle" sequence or merely the off cycle. Operation of the normally open oii cycle switch 30 either manually or by means of conveyor rails applies 24 volts to relays RL16A, B, C, D, E, F and 'RL27A, B, C, D, E, F. As has been fully explained above, the contacts of relay RL27 are activated at the endof the cycle to place the tester in readiness for testing for shorts in the next cathode ray tube. In this way the tube tester is automatically readied for immediate operation upon presentation of a tube.

HGURE 7 also illustrates the four stepper switches RIAB, RLSB, RL14B, and RL17B which home the stepper relays acting to maintain the readings obtained in the various checks throughout the remainder of the test cycle. ,Specifically, stepper switch RLSB is associated with the total emission check, stepper RL4B the cut off check, stepper RL17B the gas ratio zero, and stepper RL14B the gas ratio check. As will be noted from FIG- URE 7 each of the stepper relay coils RL4, RL5, RL14 and RL17 has a magnetic holding relay associated therewith. Stepper coil RL4 for example is connected to a relay RL34 having both a conventional pair of contacts a pair of magnetic contacts. Stepper relay coil RLS is similarly connected to a composite type relay RLI9 as is coil RL14 to composite relay RL25 and coil RL 17 to relay RL24. In each case the magnetic contact serves to keep its stepper coil energized so that the stepper switches. maintain their respective readings throughout the entire measuring cycle. In addition it will be noted that each of the stepper recorders is supplied with a positive DC. voltage of 24 volts which is connected to all the active contacts of each stepper switch. However,

aoo safs which actuates the stepper coil RLS. When the cycle is at an end the sweep arm of relay RLSB will be at one of the active positions indicating the value oftotal emission of CRT 14 being tested. Closing relay RLlfiA connects the arm of stepper RLSB and therefore the 24 volts applied to this stepper to relay RL19 in such a direction as to break the magnetic holding contact of that relay. The result is that the coil of relay RLS is deenergized and the sweep arm of stepper RLSB is returned to the home position contact. Stepper relay switch RL4B is similarly returned to the home position through contact RLloB connected to relay RL34. Stepper switches RLMB and RLl7B are similarly tie-energized through contacts RL16B and RL16C respectively. Relay RLle is also provided with contacts RL16E which operate to self lock this relay in the energized position until the on cycle'switch is next actuated. The operation of on cycle switches 8 and it} and the initiation of a. subsequent measuring cycle through relay RL6 has been fully described with reference to the initiation of a measuring or testing cycle.

As can be seen the present invention provides a fully automatic device for performing a series of tests on cathode ray tubes. Provision is included for recording readings on a plurality of stepper switches, with the readings being available throughout the entire remainder of the test cycle. As such the stepper switches provide a source for output to suitable permanent recording devices, for example an automatic printer, for making a permanent record of the readings obtained.

' Also incorporated into the tester of the present invention are a group of automatic reject conditions. Any one of five different conditions, i.e., low emission, low cut oii, high cut off, gas or shorts will cause the tube under test to be rejected. The display or recording device responsive to these conditions can indicate the tube directly or operate in conjunction with the mechanical marker ll shown in FIGURE 1. The low emission rejection will operate any time the emission level is below the required. minimum. This is accomplished by predetermined strapping between steppers RLSE and RIAE. These limits can .be changed at any time by the insertion of a different strap plug.

, All stepper relays can be checked for speed control by cycling the unit to the off position and advancing each stepper one position by hand. They should then cycle automatically to the home position. Likewise the emission potentiometer can be pre-set by removing relays R1212 and RL3. Then the on cycle switch 10 is pushed and relay RLSA advanced one position at a time through the 26th position.

All tester components are commercially available items. By way of example only, all twin triodes shown may be 6SN7s. The low and high limit meter relays RL2, RL9, RL21 and RL23 are commercially available contact meter relays.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicatedby the appended claims rather than by the foregoing description, and all changes which come within the meaning andrauge of equivalency of the claims are therefore intendedto be embraced therein.

V What is claimed and desired to be secured by United States Letters Patent is: r

l. A tube tester comprising a bridge circuit, means for applying test voltages to a cathode ray tube to produce an output signal indicative of the emission characteristics of said cathode ray tube, means for applying said output signal to one side of said bridge circuit, a stepper switch for applying a stepwise increasing reference signal to the other side of said circuit, and magnetic means connected to said stepper switch to hold it in its final position for recording the reading of said reference signal when said bridge is balanced.

2. A tube tester comprising first and second bridge circuits, means for applying test voltages to a cathode ray tube to produce a first output signal indicative of the emission characteristics of said cathode ray tube, means for applying test voltages to said cathode ray tube to produce a second output signal indicative of the cutoff characteristics of said cathode ray tube, means for initiating a test of said emission characteristics by applying said first output signal to one side of said first bridge circuit, means for applying a step-wise increasing reference signal to the other side of said first bridge circuit, means for recording the discrete value of said reference signal when said bridge is balanced, and means responsive to balance of said first bridge circuit for initiating a test of the cut off characteristic of said tube.

3. A tube tester comprising first, second and third bridge circuits, means for applying test voltages to acathode ray tube to produce first, second and third output signals indicative of the cathode emission, cut off and gas ratio characteristics respectively of said tube, means for applying one of said output signals to one side of said first bridge circuit to initiate a test, a stepper switch for applying a stepwise increasing reference signal to the other side of said first bridge circuit, means for recording the discrete value of said reference signal when said first bridge is balanced, means responsive to balance of said first bridge for applying another of said output signals to one side of said second bridge circuit, a stepper switch forapplying a step wise increasing reference signal to the other side of said second bridge circuit, means for recording the discrete value of said reference signal when said second bridge is balanced, and means responsive to balance of said second bridge circuit for applying the third of said output signals to said third bridge circuit to initiate a third test.

4. A tube tester according to claim 3 wherein said stepper switches comprise a plurality of segmental stationary contacts swept by a movable contact to apply discretely larger reference voltages supplied to each of said stationary contacts to said bridge circuits by way of said movable contact.

5. A tube tester according to claim 4 including means responsive to balance of said third bridge circuit for ending the test sequence.

References Cited in the tile of this patent UNITED STATES PATENTS 1,560,864 Schofield Nov. 10, 1925 1,771,915 (Jarnpbell July 29, 1930 2,278,697 Gould Apr. 7, 1942 2,508,424 Rouy May 23, 1950 2,760,151 Andrews et al. Aug. 21, 1956 2,845,597 Perkins July 29, 1958 2,906,943 Garman Sept. 29, 1959 OTHER REFERENCES Picture-Tube Testers, Reactivators, article in Radio- Electronics, September 1952, pp. 28-31. 

